Melt margarine and chocolate in the microwave at 30 second intervals, until completely melted, stirring in between. Beat in sugar and eggs. Mix in flour, cocoa powder, and salt, followed by the vanilla and chocolate chips. Spread evenly into the prepared pan.

In a separate bowl, beat the cream cheese, egg yolk, sugar, and vanilla until smooth. Distribute the cream cheese mixture in 8 dollops across the top of the brownie mixture. Take a dull knife and swirl the cream cheese mixture with the chocolate batter.

Bake for 35 minutes, or until the batter in the center of the pan feels just set. Let cool, then cut into squares.